Process of making viscose



A118 9 1932 R. THURM PROCESS OF MAKING' VISCOSE Filed oct. 2e. 1931" .PZzJAV .urimr OIF Magni hun Il 5.1.1.1.

INV ENTO'R Patented Aug. 9, 1932 UNITED STATES vParrala'ri \ol' FlcE nIcIIAnD Timms, orsAeINAW, MICHIGAN, AssIeNon 'ro nAxna'rEnxINs COMPANY, INc., or SAGINAW, MICHIGAN, A CORPORATION or Nnwyonx rnocnss or MAxING viscosa Application mcd Uotober 28, 1981.. Serial No. 571,184.

the cellulose sheet from which the viscose is made and the process of spinning into rayon threads or castings into cellophane sheets. v

The prime object of this invention is to provide a process wherein several of the steps used heretofore are eliminated, thus saving considerable time in the manufacture, saving equipment, and power used to operate th1s equipment, eliminating much of thev handling, and also making larger batches than has heretofore been possible.

A further obj ect of the invention is to provide a viscose which is easily filterable and which will produce' a stronger, more uniform rayon thread, and a clearer more perfect sheet of cellophane. y

A still further object is to provide a process in which much `of the danger of heating and spoiling the viscose is eliminated and in which every batch will be uniform.

With these and certain other objects, which will appear later in the specification, my invention comprises the steps of the process as described and claimed in the appended claims and the equivalents thereof.

In the manufacture of viscose, the cellu lose comes to the plant in the form of flat sheets resembling cardboard, whichj are about 16" x 18" in size and about .03" in thickness. These sheets are first steeped in.

an aqueousv solution containing. about 18% by weight ofsodium hydroxide. The sheets,

before soaking, are of the same general size and appearance irrespective of whether the cellulose is made from wood pulp by the' sulphite process or from cotton linters treated t witha sodium carbonate solution.

The soaking is 'generally done in sheet metal steeping tanks of various designs. In most instances the/tank is provided with a press plate connected to a hydraulic press piston.A The sheets are generally stacked vertically in the tank with a perforated metal. sheet between every 30 or 40 sheets and the lye solution is then admitted. These perforated plates preserve the shape of the soaked cellulose sheets and also assist in letting out the excess lye solution when the sheets are later pressed with the hydraulic piston.

This soaking process requires` about one hour after which the hydraulic i iston presses out the excess lye to such a egree that the iinal material contains about 2 to 3 pounds of lye solution for each pound of the original drycellulose.

e In the former processes the pressed cellulose sheets were charged into Shredders of various designs, which shredded the cellulose into a white fluy mass. This shredding process required about two hours, and it was necessary to watch this process very closely, as any temperature rise above 25 degress centi rade was detrimental to the final product; t erefore, these Shredders had to be jacketed and cooled by circulating water or brine.

In the shredding operation the size of the i batch was considerably limited owing to the temperature rise in the material due to the friction of the shredding blades and the necessity of bringing the material in rapid contact with the cooled walls of the' shredder.

As any increment in the size of the shredder greatly increases the capacity in proportion to the increased area, experience has l v When suiiciently aged, the cellulose was charged into xanthating drums where a measured of weighed quantity-of liquid carbon f disulphide was then admitted. In these drums the material was-tumbled about at a temperature of about 25 degrees centigrade inA contact with the carbon disulphide, both inthe liquid and vapor phase. Very shortly after the carbon disulphide hadbeen added the originally pure white matcrlal took on an intensely yellow color, caused by the reaction of the carbon disulphide with the shredded soda cellulose. As the reaction progressed, the fluffy material settled more and more, and the mass became denser and 1n the form of lumpy dough, dueto the tumbling action of the drums.

The xanthate, thus formed, has a crust or denser skin on the outside of the lumps which prevented the carbon disulphide from properly acting on the center and which crust, being diflicult to dissolve 1n the .later stages, left minute particles in the finished product which were hard to filter, and consequently owing to this and other unknown conditions all batches were not uniform and many batches were lost entirely.

The excess carbon disulphide was then removed after about two to three hours by applying vacuum to the xanthating drums. This step in the process'had to be done very carefully because the vapor of carbon d1- sulphide is very explosive when mixed with air.

After removal of the excess carbon disulphide the nished xanthate was immediately dissolved in a dilute lye solution. This dissolving process required considerable additional time and care as well as special machinery to thoroughly dissolve it, and it was rapidly circulated in the lye solution as well as sheared in order tofacilitate rapid dissolution and insure a lump free viscose. From this process the finished material went to the filters, further aging, and spinning or casting machines which converted it into the finished product.

The many advantages and values of my invention over lthe above process will be apparent when compared with the following description of my new process.

In the drawing the single figure is a flow diagram showing the progress of the various materials through the several steps of the process according to my invention, the equipment used in this process being shown diagrammatically.

Referring now to the drawing, I take the cellulose sheets, soak them in sodium hydroxide for the usual time in the usual steeping tank 1 and press out the excess liquor by the usual press 2.

In actual operation the press is generally constructed as part of the tank, but for the sake of clearness I have shown the press as a'separate unit as it forms a separate step in Athe process.

The pressed sheets are then charged into aging cans 3, where they are left for about 100 hours at a temperature of 25 deg. centia e. After the cellulose sheets have been properly aged, they are charged into a mixing and kneading machine of the type shown in U. S.

Patent- No. 1,632,97 5 issued June 21, 1927, to Fritz Kempter. rThis machine comprises a trough 4, having a plurality of arcuate bottoms 5 5, and a power driven kneading blade 6, coaxial y with each compartment located above the rcuate bottoms 5 5, and a rotary impeller which may be raised during the first stages of the kneading process and lowered, to agitate and thoroughly mix the material during the later stages. The mixing 20 minutes for a period of two minutes throughout this entire mixing process. The temperature of the material is regulated in proper limits by the admission of a temperature controlling fluid 'in the jacket 10, of the mixer trough 4. Y

The action of the kneading bladeson the blocks of soda cellulose will rst convert them into a loose mass which practically fills the total available space in the equipment. However, as the xanthating process proceeds, due to the gradual admission of the carbon disulphide, the mix becomes denser until finally a smooth plastic xanthate dough of uniform density is formed which is about the consistency of a stiff bread dough.' This step of the process requires about two hours.

9. The vacuum The excess carbon disulphide is now removed by the application of `vacuum to the apparatus and dilute lye is gradually admitted to the xanthate dough which is under proper temperature control. As the dough begins to thin down and form a semi-liquid, the speed of the kneading blades is increased to approximately twice the speed used in the first stagef of this step.

The impeller blade 7, is then lowered into the liquid andv with this combined stirring action of the impeller blade 7, and kneading action of the mixing blades 6, the xanthate is converted into a liquid, smooth, lump free viscose which is now ready for the filtering, further aging, and spinning or casting process.I

The addition of the carbon disulphide and dilute `lye to the mass is so gradual that it is thoroughly incorporated by the mixing and stirring blades and consequently the minute lumps -found in the viscose made by other processes l are entirely eliminated.

By the above process I have been enabled to produce a viscose in a much shorter time than has been done heretofore.

I have eliminated several of the steps in the process, particularly the shredding process with its inherent dangers of overheating and limitation of batch size. I have also eliminated the Xanthatng drum, the explosive hazards attendant upon their operation and the formation of lumps and their crusts which tend to make batches of irregular quality. The dissolving process used heretofore has also been eliminated, and With it the inherent diiiiculty of eliminating the minute lumps Which are difficult to filter, and as some of the lumps find their Way through the filters the spun thread is greatly weakened.

I have also saved much time by the elimination of a great deal of the handling required, to transfer the material from one piece of equipment to another, removed many of the dangers of spoiling the batch by overheating, and have enabled the manufacturer to handle larger batches, and at the same time I have produced a viscose in which all batches are uniform, which is easily fllterable, and from which a cleaner and stronger rayon thread and a clearer more uniform sheet of cellophane may be manufactured.

Having thus described my invention, what I claim and desire to secure by Letters Patent is: l. The process of making viscose which consists in soaking cellulose sheets in sodium hydroxide, pressing out the excess sodium hydroxide, aging the soaked and pressed cellulose sheets, kneading the aged cellulose in a vacuum while gradually adding carbon disulphide until the cellulose forms a stiff xanthate dough, removing the excess carbon disulphide by vacuum, gradually adding to the Xanthate dough a dilute caustic soda solution while kneading until the Xanthate becomes semi-liquid and then stirring yand kneading at increased speed until all the caustic soda solution has been added.

2. The process of making viscose which excess carbon disulphide by vacuum, andgradually adding a dilute caustic soda solution, While vstirring and kneading, until a smooth, lump free, uniform viscose is formed.

In testimony whereof I allx my signature.

RICHARD THURM.

consists in kncading soaked, pressed and aged cellulose sheets while gradually adding carbon disulphide until the cellulose forms a stiff xanthate dough, removing the excess carbon disulphide by vacuum, gradually adding to the xanthate dough a dilute caustic soda solution while kneading until the Xanthate becomes semi-liquid and then stirring and kneading until all the caustic soda solution has been added.

3. The process of making viscose which consists in kneading and stirring in a vacuum, soaked, pressed and aged cellulose sheets whlle gradually adding carbon disulphide dough, removing the excess carbon disulphide by vacuum, gradually adding a dilute caustic soda solution to the xanthate dough while until the cellulose forms a stiE xanthate 

